3DE_The_Human_Animal - The Human Animal The Population...

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Unformatted text preview: The Human Animal
The
Population Dynamics and
Population
Sustainability
Sustainability
Milt Saier
Dept Molecular Biology
UCSD Factors that Limit Population
Growth
Growth Density-dependent Factors Predation
Disease/ Parasites
Food Supply
Water Supply
Social Mechanisms Density-independent Factors Temperature
Weather
Natural Disasters
Natural
Man-created Global Environmental Disasters Exponential Growth
Exponential
Occurs when organisms are
Occurs
density-independent.
density-independent. Birth rate exceeds death rate. Both rates are constant.
Both Both rates are proportional to the
Both
numbers of individuals present.
numbers
CAN THIS CONTINUE
INDEFINITELY? Only as long
as r is constant!
as
Mathematical requirements:
Mathematical r=0, N does not change
r>0, N increases without limit
r<0, N decreases to 0 Exponential Growth in Nature
Exponential
Documented for:
Documented
Bacteria, yeast, insects, mice, humans, etc.
Bacteria,
However…
However… Exponential growth can NEVER be sustained
Exponential
indefinitely.
indefinitely.
Populations are eventually limited by densityindependent factors if not by density-dependent
independent
factors. Population Dynamics
Population The life span, number of offspring per adult,
The
and mortality rate at each stage of life affect
the growth rate of a population.
the
Mortality Curves: Three Types: Type I: Organisms have few young and usually die
Type
of old age.
of
Type II: All organisms have an equal chance of
Type
dying throughout their lives.
dying
Type III: High mortality when young; the few
Type
adults that survive have relatively long life spans.
adults Survivorship Curves
Survivorship r-Strategists
r-Strategists Many offspring
Early maturity
Short lifespan
Reproduce once
Small organisms
Precocial young
Little to no parental
Little
investment
investment
Type III survivorship
Type
pattern
pattern K-Strategists
K-Strategists Few offspring
Later maturity
Longer lifespan
Reproduce more than
Reproduce
once in a lifetime
once
Larger organisms
Altricial young
Much energy is
Much
invested in raising
young
young
Type I (or II)
Type
survivorship pattern
survivorship What factors determine the survival
pattern of K-strategists ?
pattern Because of long life span, K-strategists have the
Because
opportunity to overexploit resources if limits are
removed.
Population growth is determined by:
Population Reproductive rate,
Reproductive
Density of the previous generation, and
Availability of resources, e.g., the food supply. If resources in the habitat are consumed faster than
If
the rate of replenishment, the population ALWAYS
experiences an eventual crash.
experiences Reindeer of St. Matthew Island
Reindeer Reindeer were introduced on an island with no predators.
The population grew exponentially.
When the herd outstripped available resources, the population
When
crashed.
crashed. Sustainable, K-strategist population oscillations were observed until the
Sustainable,
agricultural revolution (about 8000 BC; pop’n < one million).
agricultural
Then, with agriculture, the first increase of numbers occurred (pop’n at
Then,
1 AD ~ 100 million; doubling time > 1000 yrs).
AD
The second increase resulted from the industrial/scientific revolution.
We are still in near exponential growth (pop’n now at 7.0 billion;
We
doubling time ~ 30 yrs).
doubling Overpopulation, Carrying Capacity, and
Time Lags
Time Humans (K-strategists) are designed to produce few
Humans
young on which they must lavish exceptional care for
survival.
survival.
Now, worldwide, we produce lots of young
Now,
(250,000/day - births over deaths).
(250,000/day
While we have increased our carrying capacity with
While
technology, we have also increased our impact on the
environment.
environment.
All K-strategist populations experience time lags:
All
exponentially growing populations overshoot their
carrying capacity before experiencing population
losses.
losses. Promises of the Green Revolution of
the 60s
the Eliminate hunger and need.
Increase the Earth’s carrying capacity.
Increase productivity and yields.
Increase technological knowledge.
Distribute food and other necessities throughout the
Distribute
globe.
globe.
Indefinite prosperity for all!!!
Indefinite
THESE PROMISES WERE REASONABLE
REASONABLE
EXCEPT THAT THEY DIDN’T TAKE INTO
ACCOUNT HUMAN POPULATION GROWTH,
RESOUCE DEPLETION or HUMAN GREED.
RESOUCE The Green Revolution failed to: Curb world hunger
Fairly distribute resources Problems of the Green Revolution: Increased food supplies led to an increase in
Increased
population growth.
population
More mouths to be fed meant more would go
More
hungry.
hungry.
Increased living standards increased resource use.
Negative impacts on the environment resulted. Impact of a Population on its
Environment
Environment Impact = P x A x T
Impact P = population size
A = per capita affluence (resource consumption)
T = environmental disruptiveness of the
environmental
technologies used
technologies
Formula published by Ehrlich and Ehrlich, 1990 Differences in Resource
Consumption
Consumption 1 Child born in the US = 2 in Sweden or Switzerland
3 in Italy
13 in Brazil
35 in India
140 in Bangladesh
280 in Chad Information from Dr. Martha Groom, NCSU Zoology Department, 1998 Corrected Impact of a Population
on its Environment
on Impact = P x A x T x W P = population size
A = per capita affluence
T = environmental disruptiveness of the
environmental
technologies used
technologies
W = per capita wastage
per
Formula by Saier, 2005 (unpublished)
Formula Human ecologists predicted a human
population crash in the late 1900s.
population
Were they right or wrong?
They were both right and wrong.
They
They were right to predict a population
crash, but they got the time constant
wrong.
wrong.
Skeptics took their error to mean that
Skeptics
the entire concept was wrong! They
concluded we have nothing to worry
about. We can live high on the hog!! BUT:
BUT:
The Human Animal
The
is subject to all of the
laws of Nature,
including those of
Population Dynamics
Population One and only one humane
solution is available to save us
from the pending disaster:
POPULATION REDUCTION
FOR
FOR
EARTH PRESERVATION 1, On what major issues did
Darwin prove to be correct?
Darwin
2, Plz describe the causes of an
2,
organismal population crash.
organismal
3, Why is it appropriate to refer
3,
to humans collectively as “the
Human Animal”?
Human
4, Contrast a K-strategist with
4,
an r-stategist.
an
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